Process for making sulphite pulp from douglas fir and other resinous conifers



Patented May 19, 1 931 UNITED STATES PATENT." OFFICE HENRY BENSON, OF SEATTLE, WASHINGTON :rnocnss FOR MAKING SULPHITE rum FROM DOUGLAS rm AND OTHER mmous comrnns No Drawing. Application filed July 27,

My invention relates to a chemical treatment of pulp chips of Douglas fir and other resinous conifers whereby they can be used in the sulfite process for making pulp 6 It is well known that certain resinous 10 tracted with alcohol-benzene solvents for the to such an extent as to make it removal of resins, is cooked under identical conditions as for spruce, hemlock, etc., the removal of noncellulose material is only partial. It. 'is .thus demonstrated that Douglas fir eontains certain organic componentspther than resins which are insoluble in su-lfite acid'cooking liquor and which cannot be removed along with the lignin in the cooking process. Such insoluble compounds produce discoloration and weaken'the pulp noncommercial.

On the other'hand, it has been found that pretreatment with hot fixed alkali, although successful in removing the resins, introduces another adverse condition in reacting with noncellulose material, vduring the preheatity of the resulting pulp.

ing, to form insoluble compounds which cannot be removed subsequently by the .sulfite cooking liquor. Although this method has often been tried experimentally, it is nowhere inuse commercially due to the inferior qual- It is also a'matter of common knowledge that cold volatile alkali is effective in the has not been economical due to the necessity of finely subdividing the wood by mechanical action in order that penetration of the volatile alkali can be obtained. Such mechanical crushing adds to the cost and weakens the final pulp, thus making the process noncommercial.

1f volatile alkali is used under pressure at too high temperatures, the process is also adversely afiected in that alteration of both cellulose and of noncellulose components i ma occur and. further that upon release of 'suc pressure from the hot hatch, decomposition occurs of the volatile alkali resinates and 1929. Serial No. 381,679.

other compounds, precipitating them within the pulp chips and contaminating the resulting pulp from the-sulfite cooking to such an extent as to make it of inferior quality.

The essential factor in my process is the discovery of a temperature that is least favorable to such alterationof the com onents, that will not cause decomposition o the reacting products, that will make it possible to secure sufficiently rapid penetratlon and that will make itof practical .use.

-For these purposes I treat the pulp chips with a dilute volatile alkali liquor at a temperature below the decomposition point of cellulose, viz., below 150 0., and above the decomposition point of the volatile alkali salts as measured at ordinary atmosphericpressure, viz, above 70 C. The temperature I have found most practicable for quickness of penetration and the other pu os'es above stated is substantially 100 C. y circulating a dilute solution of ammonium hydroxide at this temperature and under the pressure developed in the closed system, I have secured an almost complete removal of the resins contained 'in Douglas fir together with an equal or greater amount of nonresinous material, which by chemical tests is shown to be of an acidic nature, resulting, when treated with fixed alkali, in the formation of colored solusubstantially 70 C. before its'release from the digester and washing the pulp with water at the same temperature. 1 The application of my discovery to the process of making pulp from Douglas fir chi s may be better noted by a descrlption of t e steps followed throughout the process. After the pulp chips are placed in the digester, the latter is closed and, by the usual venting system for the displacement of air, hot ammonium hydroxide solution is continuously circulated over the chips. After sub-' stantially complete extraction of resins, tannins, coloring matter, etc., is effected, the heat as the draining'and washing of t is shut ofl' and the circulating ammonia salt aqueous solutions at temperature substansolutions are allowed to cool substantially tially at 100 6., the subsequent substantial below 70 C. The chips still in the di ester cooling of the solutions, substantially to 70 are next washed with warm water at or elow 0., beIore release is made of pressure, and

5 the temperature cited. The sulfite acid cookthe draining and washing of the chips sub- 7 ing liquor is next added and the cook comstantially at 7 0 C. pleted in the usual way. r Y HENRY K4. BENSON.

As the result of experimental batches, I

' have found that when pulp chips have been 3 thus subjected to the action of ammonium hydroxide or other volatile alkali and then cooked with the usual cooking liquors under the usual conditions of concentration, temperature, pressure'and time, theresulting 1 pulp shows that the pretreatment with am monium hydroxide was a true noncellulose part lignin removal; that chips thus pretreated required less cooking time with thenormal cooking liquor; that the pulp prepared from such pretreated chi s was substantially free from coagulated resinous and other non cellulose matter; that when subjected to the proper cooking, it has the same or greater strength than the unextracted pulp; and that it-consisted of substantially pure cellulose, requiring a very low bleach consumption for the final product. I

What I- claim is as follows 1. The improvement in processes of pre 30 treatment of Douglas fir and other resinous coniferous chips with volatile alkali to eliminate resins, coloring matter and other noncellulose materials contained therein so that the chips can subsequently be treated with as sulphite solutions to manufacture pulp, comprisin the circulation over uncrushed chips 1n enc osed systems of volatile alkali aqueous solutions at temperatures of 7 O-150 (1., the

' subse uent substantial cooling of the solutions fore release is made of pressure, andi the draining and washing of the chips substantially at 70 C.

r -2. The imfprovement in processes of pretreatment 0 Douglas fir and other resinous 5 coniferous chips with volatile alkali to elimi na-te resins, coloring matter and other noncellulose materials contained therein so that the chips can subsequently be treated with sulphite solutions to manufacture pulp, comprisin the circulation over uncrushed chips m enc osed systems of ammonium hydroxide I solutions at temperatures of 7 0-150 (3., the subse uent substantial coolin of the solutions fore release is, made of pressure, and

e chips substantially at C.

3. The improvement in processes of pretreatment of Douglas fir and other resinous coniferous chips with volatile alkali to elimiee nate resins, coloring matter and other noncellulose materials contained therein so that the chips can subsequently be treated with sulphite solutions to manufacture pulp, comrising the circulation over uncrushed chips I m enclosed systems of dilute volatile alkali 

